Refactor ranges::minmax and ranges::minmax_element #3384
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The fix for microsoft#2900 in microsoft#3366 did not take advantage of the fact that the minimum and maximum elements of a range are always distinct except when the range has only one element. It couldn't easily do so due to the way `ranges::minmax` and `ranges::minmax_element` share the common backend `ranges::_Minmax_element_unchecked`. This PR introduces a new backend for `ranges::minmax` (`ranges::_Minmax_fn::_Minmax_fwd_unchecked`) and makes `ranges::_Minmax_element_unchecked` the private member `ranges::_Minmax_element_fn::_Minmax_element_fwd_unchecked`. Since the two are distinct, `_Minmax_fwd_unchecked` can deal in values instead of iterators, and we can unroll the first loop iteration to detect the single-element case naturally. Since no additional branch is needed, we can enable the fix for microsoft#2900 unconditionally. Drive-by: Fully qualify the names of ugly functions called by `ranges::minmax` and `ranges::minmax_element`.
AlexGuteniev
approved these changes
Feb 3, 2023
fsb4000
reviewed
Feb 4, 2023
fsb4000
reviewed
Feb 7, 2023
StephanTLavavej
approved these changes
Feb 9, 2023
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I'm mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed. |
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Thanks for overhauling this code to inherently handle the unusual corner case! 😸 📈 🎉 |
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The fix for #2900 in #3366 did not take advantage of the fact that the minimum and maximum elements of a range are always distinct except when the range has only one element. It couldn't easily do so due to the way
ranges::minmaxandranges::minmax_elementshare the common backendranges::_Minmax_element_unchecked.This PR introduces a new backend for
ranges::minmax(ranges::_Minmax_fn::_Minmax_fwd_unchecked) and makesranges::_Minmax_element_uncheckedthe private memberranges::_Minmax_element_fn::_Minmax_element_fwd_unchecked. Since the two are distinct,_Minmax_fwd_uncheckedcan deal in values instead of iterators, and we can unroll the first loop iteration to detect the single-element case naturally. Since no additional branch is needed, we can enable the fix for #2900 unconditionally.Drive-by: Fully qualify the names of ugly functions called by
ranges::minmaxandranges::minmax_element.